A Tale of Two Seabird Cities

Caroline Bateson shares with us her experiences of Cemlyn and South Stack

A Tale of Two Seabird Cities 

On the furthest north west and north eastern tips of Anglesey are two great seabird colonies – South Stack and Cemlyn.  Both are beautiful, wild and in close proximity to turbulent tide races which provide rich fishing for many seabirds. I have been lucky enough to work at both and observe these amazing places in great detail. Both South Stack and Cemlyn provide us with a unique opportunity to experience the magic of a seabird colony without needing to take a boat-ride to a remote island, where these seabirds so often choose to breed.

A seabird colony is an incredible entity in itself - one noisy body of activity, made of so many individual birds. While the seabird colonies at South Stack and Cemlyn have many similarities, they are also uniquely different – with auks (guillemot, razorbill and puffin) breeding at South Stack and terns (Sandwich, common and Arctic) at Cemlyn.

South Stack, at the north western tip of Holy Island is all vertical rock faces housing a spectacular high-rise seabird city. These hard, ancient and dramatically folded cliffs are a miracle of geology and provide perfect ledges for the breeding guillemots, which are relatively safe from mammalian predators. Like a series of random shelves, they display the guillemots and razorbills as if in a giant bookcase.

The cliffs are battered by north westerly gales, swathed in sea fogs and for a few summer months topped with a brilliance of flowering maritime heath. The summer months also see thousands of visitors swarming to see the seabirds and the views, as South Stack is a tourist hot spot. When I worked as Visitor Officer in Ellins tower I thought there was an irony in observing the lines of visitors looking across at the uniform brown and white rows of guillemots looking back at the coloured shapes of all the visitors on the cliff top.

All seabirds spend most of their lives at sea and only come to land to breed. However, there are big variations in lifestyle according to species. Seabirds typically have ‘slow’ lifestyles – with long lives, low productivity and slow chick maturity.

The auks have a particularly ‘slow’ pace of life. They live to at least 30 years – usually longer and the young birds do not return to land to breed until they’re five years old. They only come back at all to lay a one solitary egg, which they brood on their feet (like penguins do.) Both eggs and chicks are well protected by the parent birds who sit with their backs turned to the elements - creating an umbrella of protective wings over the whole colony cliff face.  Even in July, when the chicks are quite large, it’s really hard to spot them on the cliffs.

Auks are very much anchored to ‘site’ which by its nature is of hard rock, permanent and unshifting. This loyalty to place and the stable enduring nature of the site suit the very ‘slow’ paced life of auks and their strategy for survival as a species.

The physiology of auks as birds is solid and much more of sea and rock than sky. Even their calls are gurgly-gargly as if from singing deep under water. They spend all of their lives (apart from the short breeding months) out at sea, roosting on the water and diving deeply for fish from the surface. In the clear waters below the cliffs at South Stack you can see the auks diving - swimming down deeply with their wings to catch sandeels and other small fish.  Strong and graceful underwater, the rapid wing beats of flying auks are not unlike bees in flight. They’re not particularly graceful and are rarely fly too high above the sea.

When auk chicks are ready to leave the cliffs – they are called off the ledges by the parent bird before they can fly. They have to take a leap of faith from the high cliffs and flop and flutter  to the sea below. Their departure is downwards to the water and takes place in the safer dimness of the evening.

Terns are completely different – so much more birds of the air, or the interface between air and sea.The Welsh name for tern translates to English as ‘sea swallow.’  Terns are very like large white swallows with their graceful tails and slender wings, and like swallows they can a fly with dexterity low over land as well as sea. Terns can often be seen flying over land and their distinctive oily – squeaky calls announce their fleeting presence.

Cemlyn in terms of landscape is also a place of complete contrast to South Stack – with a low down, flat wateriness lying in a cocoon of low drumlinoid hills. Esgair Cemlyn, the curved ridge of blue-grey shingle is unstable as a habitat and constantly moving and shifting shape. In summer the shingle is splashed with unexpected dashes of colour – the creaky leaved sea-kale and yellow horned poppy.

The whole habitat at Cemlyn is semi-natural and those crucial little islands resting in the brackish lagoon need sensitive management in order to maintain the most important Sandwich tern colony in Wales. Common, Arctic and historically Roseate tern also breed at Cemlyn and rely on intense summer wardening for protection.  While Cemlyn is also a place of great landscape beauty, it is only the more dedicated birdwatcher or walker that makes it along the maze of lanes to this more remote location.

The terns – instead of being neatly shelved on a vertical rock-face are spread out across two flat islands, with each species in its preferred niche. When the chicks are hatched and old enough to wander around it’s easy to spot them. The Sandwich tern chicks in particular spread out over the whole island in a chaos of fluff balls. They look so exposed to predators!

In terms of pace of life, the Sandwich tern sits in the middle between land and sea birds – having what is classed a ‘moderate’ pace of life. Terns can live for roughly 20 years and have a larger clutch size of 2 to 3 eggs. The young birds will return to breed earlier too - from 2 to 3 years old. The oldest Sandwich tern on record is 23. 

Whereas auk colonies have often been in the same location since the ice age, terns, despite returning year after year to favoured places – can be much more flexible and adapt to new and increasingly man-made sites in an opportunistic way. Like the sandy and shifting unstable environments in which they nest – terns as a species are flighty and will abandon locations and move to others in order to maximise breeding success. The feel of a tern colony is of shriller calls, fluid elegance, delicate flightiness and graceful dips to the sea for fish.

When the breeding season is over the tern fledglings will ascend to the skies. Initially they disperse reasonably locally before making their long aerial migrations to the west coast of Africa and beyond. By the end of October they are gone for the entire winter. Completely different to the water-bound and flightless auk chicks, which disappear across the seas of the northern hemisphere.

While in the UK, both sites are protected by conservation charities, but once they have left their survival is largely out of our hands.

What is vitally important is that both NWWT and RSPB can maintain the funds to carry out the essential wardening and conservation work necessary to ensure the survival of these seabirds into the future. Both South Stack and Cemlyn are facing threats from renewable energy developments in addition to the unpredictable challenges presented by climate change. We need to revere and enjoy these most magnificent places and do everything in our power to protect all our seabirds into the future.

©Caroline Bateson